In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Grinding and milling machines typically include several pick holders mounted on a rotating drum. The pick holders are removable from the drum for maintenance or replacement. Each pick holder holds a rotatable tool pick that rotates within the pick holder during operation. The pick holder has a bore for receiving a shank of the tool pick and a barrel at its frontward end on which a shoulder of the tool pick may be seated. A common type of pick holder includes a polygonal-shaped (e.g., hexagonal) barrel to facilitate installation and removal of a pick. Each tool pick has a tip portion that contacts the surface of material that is to be ground or milled. To maximize the working life of the tip portion, and thus of the tool pick, the shank of the tool pick is able to rotate within the bore of the pick holder, so that the tip portion of the tool pick wears substantially uniformly.
During operation of the machine, debris such as fines, dust, grit, pebbles, dirt, and the like, may work its way between the shoulder of the tool pick and the barrel of the pick holder, abrading the barrel of the pick holder. While the tool pick is readily replaceable and needs periodic replacement due to wear of the tip portion, it is preferable not to have to replace the pick holder frequently. Because debris can also cause the pick holder to itself become lodged in the drum, a polygonal shaped barrel may be provided at the forward end of the pick holder to enable use of a wrench or other tool to rotate and dislodge the pick holder from the drum.
The debris may also get into an annular gap between the bore of the pick holder and the shank of the tool pick, impeding rotation of the tool pick, which reduces the wear life of the tip portion of the tool pick. Therefore, to protect the barrel of the pick holder and to help preserve the ability of the tool pick to rotate during operation, there is a need for a mechanism to prevent or reduce frictional wear from debris on the barrel of the pick holder, and to prevent or inhibit debris from reaching the annular gap between the shank of the tool pick and the bore of the pick holder.